Brief Answer:
yes, this is the presentation of this 
hernia.
Detailed Answer:
Hi, 
Thanks for writing to XXXXXXX  This is Dr. Ashish Verma, a 
general surgeon, answering to your query.
The lump that has popped up under your 
sternum is your stomach which has herniated into your 
thoracic cavity through the defect in your diaphragm, so the effective volume of your stomach had reduced leading to loss of appetite, also the stomach portion in your thoracic cavity is compressing upon your lungs, leading to 
shortness of breath.
If the shortness of breath increase, I would suggest that to show in the emergency room.
Your hernia, needs surgery, and the earlier you get it done, the better it will be.
Hope, that I have answered to all your queries. If you have further queries, I will be glad to answer them.
Regards,
Dr. Ashish Verma